In general, audio signals include signals of various frequencies, the human audible frequency ranges from 20 Hz to 20 kHz, and human voices are present in a range of about 200 Hz to 3 kHz. An input audio signal may include components of a high-frequency zone of 7 kHz or higher in which human voices are hardly present in addition to a band in which human voices are present.
In recent years, users' demands for advancement of networks and high-quality services have increased more and more. Audio signals are transmitted via broad bands such as a narrowband (hereinafter, referred to as “NB”), a wideband (hereinafter, referred to as “WB”), and a super wideband (hereinafter, referred to as “SWB”).
In this regard, when a coding method suitable for an NB (with a sampling rate up to about 8 kHz) is applied to WB signals (with a sampling rate up to about 16 kHz), there is a problem in that sound quality degrades.
When a coding method suitable for an NB (with a sampling rate up to about 8 kHz) or a coding method suitable for a WB (with a sampling rate up to about 16 kHz) is applied to SWB signals (with a sampling rate up to about 32 kHz), there is also a problem in that sound quality degrades.
Therefore, development of voice and audio encoder/decoder has progressed which can be used in various bands of an NB to a WB or an SWB or in various environments including communication environments between various bands.